2nd home location: Sonoma Coast or SF Bay area?

[Robert Fisher]

I am thinking about buying a second home.  I will retire in maybe 15-20 years, and would like to live in the Sonoma Coast part time if not full time.  So I need a property there.  

I'm thinking about buying it now; hopefully the property tax will be lower than when I buy it in 15-20 years.  But the region's price appreciation seems to lag behind SF Bay area.  I'm in a real dilemma.  Should I buy at the coastal area now, or should I buy in SF Bay area now, then in 15 years switch over to coastal area?  Can you give me some pros and cons?